Always the best way is to keep things simple. The more complex the more expensive and the higher the error rate. So I think just putting soil on your modules is the way to do it.

Regarding the solid-liquid-material: I know that there are bullet-proof vests available that are elastic or like liquid until a projectile hits the material. Then the fabric becomes rigid and stops the bullet.

_________________"The hardest hurdle to space isn't the technicalities and money. But rather, the courage and the will to do it." - Burt Rutan.

The point is that they have to be working which menas to fir into their task. The task itself already tends to force a minimum of complexity. In so far thinbgs mustn't be kept simple but they should be kept as simply as possible.

This I am mentioning only because each issue like the KISS-principle etc. is sounding to me as if the purpose or task might have been lost out of focus.

This moment the thought came up to me that the existence of martian caves might point to an additional danger threatening habitats. The ground below them might hide a cave instead of massive ground.

So it might be required to investigate if there is a cave below the habitat (I have in mind habitats for colonists at present that may be heavy). One solutions might be to connect the habitats by tethers to points that are higher than them. Then they could hang from them if the ground breaks.

The next question is if habitats located inside caves are secure. each asteroid hitting the ground around the entrance of the cave might make this ground to go down into the interior of the cave and destroy the habitat there.

I'd expect that the site for a habitat and first colonial base would have been sufficiently investigated for this very problem. I'mnot sure what the geology is like, but if it's even remotely similar to the Earth, then large caves close to the surface would be fairly low risk. The additional danger of having a cave in due to a meteor strike on the surface above a cave sited habitat is real, but I'd suggest much better than a surface habitat receiving the very same impact. I wouldn't want to be there in either case. Actually scratch that, yes I would. In a pressure suit of course, but how cool would it be to survive that?

With regard to excavating habitats, perhaps some locations may favour this over others. Look at some parts of France, where there are still towns build into excavated caves / habitats. Australia too! Just down to conditions I guess. Perhaps a temporary module to live in while the occupants get on with the building of a more permenant solution. Have you seen The Thing? In it, their arctic habitat was on two levels, with the lower level being under the surface.

What about investigations of regional crater frequencies? I have in mind looks to the frequency of craters of certain ages. If they arenâ€™t distributed equally regions of less risk of impact can be distinguished from others.

And in particular present impacts could be observed by particular cameras, sensors etc. or an entire particular probe â€“ in order to prepare a permanent martian base or even settlements and colonies.

By uploads and downloads the probe itself might more easyly and quickly identify new craters and impacts â€“ and it could identify links to meteor swarms, comets etc.

What about investigations of regional crater frequencies? I have in mind looks to the frequency of craters of certain ages. If they arenâ€™t distributed equally regions of less risk of impact can be distinguished from others.

I think that it will be more important to find out what the geology and weather patterns are like in any potential Mars base site.

_________________A journey of a thousand miles begins with a single step.

Regional differences in crater density are due to geological processes that erase the craters working at different speeds in different regions and are not due to different impact rates. Impact rates are uniform all over the planet. This is the case for all planets and moons.

So what about using them as protection for martian habitats as well? Is temperature of meaning here? If yes "Wurtzit-Bornitrid" might fit better into it because it can resist to higher temperatures when exposed to the air - but I do not know if this is valid in the carbondioxyde atmosphere of Mars also.

The materials are that rare that they have to be produced which is considred to be of interest.